Republican Mitt Romney is standing behind Indiana Senate hopeful Richard Mourdock as President Barack Obama's campaign keeps up criticism of Romney's ties to a candidate who said pregnancies that result from rape are "something God intended."

Republican Mitt Romney is standing behind Indiana Senate hopeful Richard Mourdock as President Barack Obama’s campaign keeps up criticism of Romney’s ties to a candidate who said pregnancies that result from rape are “something God intended.”

Romney’s campaign has said he disagreed with Mourdock’s remark, which came in a debate Tuesday with his opponent, Rep. Joe Donnelly. But Romney is standing by his endorsement of Mourdock – and not asking the Indiana state treasurer to take down an ad Romney filmed Monday in support.

The remark thrust a contentious social issue back into the presidential race as Election Day draws near. Early voting has begun in many states, and Obama himself plans to vote Thursday in Chicago. It’s an inopportune time for Republicans, who had been seeing gains in polls among female voters critical to a Romney victory. Democrats are eager to link Romney and other Republican candidates to Mourdock’s remarks.

“Romney must withdraw his support of Mourdock- who’d force rape victims to bear an attacker’s child as `God intended,'” Obama’s campaign wrote on the president’s campaign Twitter account.

On “The Tonight Show” Wednesday, Obama criticized Mourdock for his comments, saying “rape is rape” and distinctions offered by the Republican candidate “don’t make any sense to me.”

Obama campaign aides see Romney’s refusal to pull his support for Mourdock as an opportunity to cast the GOP nominee as extreme on women’s health issues and expose what they say are Romney’s attempts to moderate those views for political gain.

“Romney has campaigned as a severe conservative, supports severely conservative candidates, and would be a severely conservative president – especially on issues important to women,” Obama deputy campaign manager Stephanie Cutter wrote in a fundraising plea Wednesday evening. She called Mourdock’s remarks “one of the most demeaning comments about women” from a politician.

The Republican nominee and his traveling staff spent Wednesday avoiding questions on the subject. Romney did not speak to reporters or address Mourdock’s remarks during two public appearances. His aides sometimes speak to reporters traveling on Romney’s campaign plane but did not appear Wednesday – and were scarce at Romney’s rallies. They ignored repeated emailed questions about Mourdock.

Less than two weeks before Election Day, opinion polls depict a close race nationally. Romney’s campaign claims momentum as well as the lead in Florida and North Carolina, two battleground states with a combined 44 of the 270 electoral votes needed to win. Obama’s aides insist the president is ahead of or tied with his rival in both those states and in the other seven decisive battlegrounds.

Obama was campaigning with all the signs that his presidency is on the line, crossing the country Wednesday with rallies in Iowa, Colorado and Nevada and appearing on the “The Tonight Show” in California. In the 17th hour of his day, he stood in a park on a cool, crisp night before thousands of supporters in Las Vegas. By then it was nearly 1 a.m. in Washington, where his day had begun, and Obama’s voice still boomed.

“If you’re not going to sleep, you might as well be in Vegas,” Obama said before encouraging people to cast their votes early, as Nevada law allows. He met later with employees at the Bellagio hotel.

On Thursday, Obama was so not much starting his day as continuing his last one. After spending the night on Air Force One, he’s campaigning in Tampa, Fla., Richmond, Va., and Cleveland before heading back to the White House.

In the midst of the 40-hour dash across six battleground states and eight states overall, he planned to do exactly what he is imploring millions of people to do for him: vote.

In his hometown of Chicago, Obama was scheduled to be the first president to vote early in person. By making a special trip just to cast his vote, Obama sought to build awareness about the early voting option, which is a vital part of both campaigns’ political operations.

“I can’t tell you who I’m voting for,” Obama told a crowd of thousands gathered in chilly Denver on Wednesday. “It’s a secret ballot.” He noted that his wife, Michelle, had already voted by absentee ballot and she promised she went for him.

Taken together, the nonstop travels were the busiest single stretch of Obama’s long and combative run for a second term.

He is selling a more specific second-term agenda these days and warning that Romney is untrustworthy, but increasingly, Obama’s goal is to ensure his supporters get to the polls.

Romney was waking up in Cincinnati to kick off a daylong swing through three Ohio towns, sharpening his focus on a state that’s critical to his hopes of winning the White House. The Republican’s advisers say their internal data has him tied to win the state’s 18 electoral college votes, but public polling has shown Obama with a slim lead.

Romney is working to cast Obama’s campaign as focused on small issues while the Republican ticket is focused on fixing the nation’s serious fiscal problems.

“His campaign seems to be smaller and smaller by the day,” Romney told more than 2,000 people in an airplane hangar off the tarmac in Cedar Rapids, Iowa, his campaign plane looming behind him. “Attacking me is not an agenda for the future.”

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Associated Press writers Ben Feller in Nevada and Julie Pace in Washington contributed to this report.